A linear light source has been increasingly used for a light source of a various type of an apparatus. The linear light source is made up of a combination of (i) a light emitting device, such as a light emitting diode (LED) or a semiconductor laser, and (ii) a linear material, such as a optical fiber, which can transmit light. The linear light source is so that light coming from a light emitting device is incident on an end of the linear material and transmitted through within the linear material so that the linear material carries out light emission (see, for example, patent literatures 1 to 3).
In some linear materials, light coming from a semiconductor laser is transmitted through within a linear material so that an illumination effect can be brought about. In this type of the linear light sources, however, there is a case that semiconductor laser light incident on one end of the linear material is directly outputted from the other end of the linear material. Since the semiconductor laser light has a high energy density, such case involves a risk that causes a danger to a human body, in particular to eyes. Therefore, it is necessary that the linear light sources using the semiconductor laser include a structure for avoiding the risk.
An example of the linear light source including the structure encompasses an illumination apparatus of the patent literature 4 in which a light emitting device is provided within a optical fiber so that the light emitting device and the optical fiber are integrated with each other. In the illumination device, it is possible that light be kept from leaking, and the light emitting device and the optical fiber be combined to each other at a greater efficiency.